Calpain is one of the proteolytic enzymes in cytoplasm, which are distributed widely in living organisms, and activated by a calcium ion. At present, it has been clarified that abnormal activation of this calpain is involved in various diseases such as stroke, subarachnoid hemorrhage, Alzheimer's disease, ischemic disease, muscular dystrophy, cataract, platelet aggregation, arthritis and the like [Trends in Pharmacological Sciences, vol. 15, p. 412 (1994)]. On the other hand, it has been clarified that a calpain inhibitor is effective for maintaining transparency of a lens in an experimental cataract model by way of lens culture [Curr. Eye Res., vol. 10, pp. 657–666 (1991)], and useful as a therapeutic agent for cataract (WO93/23032) and the like. As calpain inhibitors reported heretofore, peptide halomethane derivative (JP-B-6-29229), peptide diazomethane derivative [Biochem. J., vol. 253, pp. 751–758 (1988), J. Med. Chem., vol. 35, pp. 216–220 (1992)], peptidyl aldehyde derivative (EP771565, U.S. Pat. No. 6,057,290 and the like) and the like can be mentioned. However, as the situation stands, these inhibitors have not been put to practice.